1. Field of the Invention
This invention relates to a process for effectively recovering catalysts which were used in the industrial preparation of .alpha.-(4-isobutylphenyl)propionic acid.
.alpha.-(4-Isobutylphenyl)propionic acid is a medical raw material for anti-inflammatory, analgesic and antipyretic drugs.
2. Description of the Related Arts
The present inventors have already proposed a process for producing .alpha.-(4-isobutylphenyl)propionic acid by reacting .alpha.-(4-isobutylphenyl)ethyl alcohol with carbon monoxide in the presence of a catalyst comprising a nickel compound, a phosphine compound and an iodine compound, preferably further in the presence of a ketone solvent.
In order to make the above process more economical, an additional process in which the used catalyst can be recovered and reused effectively is required to be established.
In a conventional process for recovering a catalyst used in a homogeneous reaction system, reaction products are distilled out and the catalyst is recovered as a residue.
When the above conventional recovering process is applied to the reaction mixture obtained from the said production process for .alpha.-(4-isobutylphenyl)propionic acid, the activity of the recovered catalyst was found to be markedly lowered. This is caused by the fact that the activity of the catalyst becomes deteriorated with exposure to the high temperatures because of high boiling point of the product. When the distillation is carried out at a relatively low temperature under a reduced pressure, the by-products having high boiling points are found to be accumulated on the catalyst, so that the activity of the recovered catalyst is gradually lowered.